Re: [ccp4bb]: MIR phasing

["David J. Schuller" <djs63@cornell.edu>]

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On Wed, 8 May 2002, Ram Thaimattam wrote:

> I am currently struck at the patterson heavy atom difference map interpretation
> in MIR phasing. I have a native data set with data extending to 2.65 A, and 
> two heavy atom derivatives, Uranium and Platinum have diffraction data extending
> to 3.0 and 2.9 A respectively. Scaling the three data sets (using scaleit)shows 
> good statistics. The overal R-fact for U and Pl derivative data sets are 17 and 
> 19% respectively. Furthermore there is a drop in the R-fact valuses at 4.8 A in
> both these data sets. However, when patterson heavy atom difference maps are
> calculated for these derivatives huge number of peaks are found in the map. 
> There are about significant 300-400 peaks(>3sig) in both the heavy atom 
> difference patterson maps. This is really anoying. I am not sure where exactly
> I am doing mistake. In this regard I request to kindly help me out to solve 
> this  problem.

how about looking at the SAD (single-wavelength anomalous dispersion) 
maps for your derivatives?  these should be free from scaling effects.

=======================================================================
If we started hunting "bipedal lizards through gloomy tunnels with a shotgun"
Apple might become the new SGI for crystallographers - Laurie Betts, Ph.D.
=======================================================================
                        David J. Schuller
                        modern man in a post-modern world
                        MacCHESS, Cornell University
                        djs63@cornell.edu